Ionic vacuum pump having multiple externally mounted magnetic circuits



R. L. JEPSEN April 2, 1968 IONIC VACUUM PUMP HAVING MULTIPLE EXTERNALL MOUNTED MAGNETIC CIRCUITS 2 Sheets-Sheet l INVENTOR.

OBERT L. JEPSEN i 10 RNEY Filed Feb. 28, 1966 R. L. JEPSEN IONIC VACUUM PUMP HAVING MULTIPLE EXTERNALL MOUNTED MAGNETIC CIRCUITS Filed Feb. 28, 1966 2 Sheets-Sheet I INVENTOR. R

OBET L JEPSEN I TORNEY 3,376,455 IONIC VACUUM PUMP HAVING MULTIPLE EX- TERNALLY MOUNTED MAGNETIC CIRCUETS Robert L. Jepsen, Los Altos, Califl, assignor to Variau Associates, Palo Alto, Calif., a corporation of California Filed Feb, 28, 1966, Ser. No. 530,638 10 Claims. (Cl. 313-161) The present invention relates to ionic vacuum pumps and, more particularly, to an ionic vacuum pump having a structural configuration which facilitates the construction of high speed, high capacity modular-type pumps which can easily be assembled and disassembled. Specifically, the present invention appertains to ionic vacuum pumps having an envelope defining a main chamber and at least two appendage chambers for receiving vacuum pump elements extending from one side of the main chamher, and a magnetic circuit mounted externally of the envelope associated with each appendage chamber.

An ionic vacuum pump whose pump element unit is comprised of a plurality of cells has come to be accepted as the most efiicient, high speed ionic vacuum pump. However, it was discovered that pumps with a large number of cells are not well suited for use with a single permanent magnet. This is because of the necessarily large air gap required to handle a large number of cells. To overcome this problem, generally two approaches have been followed, one of placing the magnets inside the pump envelope, and the other of providing a plurality of cellular pump element units each having a magnet associated therewith.

Most presently available ionic pumps utilizing highly efiicient magnetic circuits employ permanent magnets located internally or forming part of the pump envelope. Such a pump configuration is disclosed in the U.S. patent application S.N. 383,681, now abandoned, filed July 20, 1964, entitled, Magnetically Confined Glow Discharge Apparatus, of which I am a co-inventor with John C. Helmcr. Outgassing such internally arranged magnets is difficult, time consuming, and often imperfect since magnets are constructed of poor vacuum material, i.e., they tend to be porous and dirty. As a result of imperfect outgassing, contaminating gases often are released, i.e., outgassed during a pumping operation. This undesirable outgassing has prevented such pumps from rapidly attaining pressures lower than 10- torr.

To prevent such outgassing, internally located magnets have been enclosed in gas-tight cans constructed of nonmagnetic material. One such U.S. Patent 3,117,247. However, even the internally located canned magnet structuresoutgas excessively. In fact, if the internally located canned magnet structures are allowed to cool slowly after 'bakeout, the o-utgassing therefrom will dominate the pumpdown performance of the pump. Hence, it has become the practice to rapidly cool the interior of such pumps in order to reduce the outgassing rate and thereby enhance the pumpdown perfonmance of the pumps. Cooling the pump interior to the required extent is accomplished only with great difliculty and inconvenience.

Often it is necessary to remove and replace internally located magnets, for example, in order to recharge the magnets. The removal of internally located magnets is difiicult and generally, can be accomplished only by disassembling the vacuum pump. Of course, such disassembling requires pump shut-down since the interior of the pump must be exposed to atmospheric pressure. By 10- cating the magnetic circuit outside of the envelope of the vacuum pump, the magnetic circuit components can be removed easily without disturbing the internal vacuum pump is described in my States Patent 3,376,455 Patented Apr. 2, 1968 conditions of the vacuum pump envelope. Furthermore, the inconveniences concomitant with cooling internally located magnetic circuit components are eliminated.

For the forementioned reasons, some prior art ionic vacuum pumps have been designed utilizing magnetic circuits mounted externally to the pump envelope. One such prior art ionic vacuum pump is described in U.S. Patent 2,983,433 to Lloyd et al. Configurations such as disclosed by the Lloyd et al. patent incorporate a magnetic soft iron pole piece parallel and in proximity to each cathode of the two parallel cathodes of each pump unit. One pole face of each of a pair of magnets is positioned adjacent a pole piece of a pump unit so that the internal magnetic field of each magnet is at right angles to the gap between the two parallel cathodes. To provide the necessary magnetic field in the cap between the cathodes, the polarity of the pole face adjacent one cathode is opposite that adjacent the other cathode of the pump unit. Hence, the other opposite polarity pole faces of the magnets are remotely located from the pole pieces of the pump unit. To complete the magnetic path for the magnetic flux extending between the pair of magnets, a plurality of similar assemblies are arranged to define a closed magnetic circuit therethrough. The closed magnetic circuit is completed by arranging each magnet to have its remotely located pole face of an opposite polarity at the remotely located pole face of the most proximate magnet of the adjacent pump unit. If the magnetic path is not completed in the manner specified, an external yoke of soft iron, which is heavy, cumbersome, and expensive, is employed to reduce the resistance of the magnetic circuit and thereby increase the magnetic field in the gaps in which pumping elements are located, and to reduce fringing or leakage magnetic fields.

Other limitations are inherently characteristic of such prior art ionic vacuum pumps. Because opposite poles of different magnets face towards each other, large magnetic forces exist which tend to draw them together and thereby hold the magnets tightly against the pole pieces and pump envelope. If the magnets are removed individually from the pump envelope, and then subsequently brought back into position, a significant reduction in magnetic field (due to partial demagnetization of the magnets) will, in most cases, have occurred. To obtain the maximum magnetic field available from the magnets in their magnetic circuit, it generally requires remagnetization-often a tedious and costly process.

On the other hand, if the magnets are removed from the pump envelope together, care must be taken to maintain them in their same proper positions relative to one another as when in use. For these reasons, when recharging the magnets or placing them in position about the pump envelope, it is common practice to use specially designed jigs for holding the magnetic circuit in the same topographical position as when the pump is in use. In those cases where jigs are not used, the magnets are recharged after the magnets are placed in position about the pump envelope. In any case, the required recharging process is diflicult, inconvenient, and costly.

In attempting to eliminate the problems characteristic of ionic vacuum pumps of type described in the Lloyd et al. patent, various other configurations have been developed. For example, a disc shaped pump with magnets disposed radially about the circumference is described in U.S. Patent 3,125,283 to Zaphiropoulos et al. However, to remove the magnets from such a pump still requires at least some separation of the magnets, leading again to a partial loss of magnetization upon reassembly. Another approach to the problems is described in the U.S. Patent 3,216,652 to Knauer. However, as noted in my U.S. Patent 3,094,639, the pumping characteristics of ionic vacuum pumps are optimized by confining the glow discharge to a plurality of paths within a given space through which a magnetic field permeates. Generally, this is accomplished by providing a cellular anode structure defining individual compartments within which a glow discharge takes place. Because of the curved magnetic field configuration characteristic of the Knauer pump, practically speaking, it would be very ditficult and expensive to construct such a pump having a cellular anode structure. This is because each cell of the cellular structure would have to be curved to conform to the particular curvature of the magnetic field found at the location of the cell.

Accordingly, it is an object of this invention to provide a modular-type ionic vacuum pump capable of being assembled and disassembled easily which can rapidly attain pressures lower than torr.

More particularly, it is an object of this invention to provide a modular-type ionic vacuum pump having a plurality of magnets any of which could be removed from the vacuum pump without detrimentally affecting the operation of the pump.

Another object of this invention is to provide a modular-type ionic vacuum pump whose interior is not required to be cooled during pump bake-out operations.

It is still another object of the present invention to provide a modular-type ionic vacuum pump employing magnets mounted externally of the pump envelope which can be removed therefrom and replaced without undergoing significant irreversible loss in magnetization.

A further object of this invention is to provide a modular-type ionic vacuum pump employing a plurality of magnets whose total tlux leakage is reduced to the greatest degree practical.

Yet a further object of this invention is to provide a modular-type ionic vacuum pump employing a plurality of magnet circuits in an arrangement whereby a large portion of the normally considered leakage flux of each magnetic circuit permeates the region of the Working field of adjacent magnets to enhance the working field established therein.

It is yet another object of the present invention to provide an ionic vacuum pump employing a magnetic circuit which can be magnetized easily with a simple coil configuration.

The present invention is an ionic vacuum pump of a unique configuration whereby the aforementioned objects and advantages are realized. According to the present invention, a permanent magnet is mounted externally of a pump envelope with its internal field extending at right angles to the planes within which parallel pump cathodes are positioned. Two pole pieces are provided, one extending from each pole of the magnet parallel to each cathode, for coupling the magnetic field from the magnets to the gap between the cathodes, thereby establishing a working field therein. A vacuum pump unit is completed by positioning a partitioning means in the gap between the cathodes to define therein compartments wherein glow discharges take place. A module is formed by stacking two pump units together, each contained in individual spaced-apart appendage chambers, preferably, parallelly extending from one side of a main chamber, with adjacent magnetic poles of adjacent magnets being of the same polarity.

By arranging the magnets external of the pump envelope to extend across the gap defined by the two cathodes of each pump unit with the adjacent magnetic poles of adjacent magnets of the same polarity, the present ionic vacuum pump can be assembled and disassembled easily. Most importantly, however, any of the magnetic circuits associated with a pump unit can be removed easily without detrimentally affecting the operation of the remaining pump units. Furthermore, if the magnetic circuits are removed and replaced about the pump envelope in pairs, the amount of magnetization lost by the magnetic circuits will be insignificant. In fact, a single magnetic circuit can be removed and replaced a few times by itself without detrimentally altering its degree of magnetization. This is a very important advantage of the pump of the present invention when it is considered that the magnets may be charged while demounted from the pump and placed in position about the pump envelope without having to use special jigs, thereby facilitating the stacking of modules. Moreover, as will become clearer from the description infra, the unique arrangement of the plurality magnetic circuits relative to one another results in the fields generated by adjacent magnets cancelling in the space therebetween while aiding in the gap,

between the pole pieces of each magnets adjacent magnets. Because of this unique field orientation interrelationship, the working field is enhanced while the losses due to flux leakage reduced, leading to more efficient use of the permanent magnet material.

The aforestated and other objects and advantages of the ionic vacuum pump of the present invention will become more apparent upon consideration of the following description of selected embodiments thereof taken in connection with the accompanying drawings of which:

FIG. 1 is a top view of one embodiment of the basic ionic vacuum pump module of the present invention.

FIG. 2 is a front elevation view taken at lines 2-2 of FIG. 1.

FIG. 3 is a perspective view showing a preferred pump element configuration as arranged within the working magnet field generated by the magnetic circuit of the vacuum pump.

FIGS. 4-7 portray some of the various ionic vacuum pump embodiments constructed in accordance with the present invention.

Considering FIGS. 1 and 2, the basic module of the ionic vacuum pump of the present invention includes a tubular envelope 11 of stainless steel or other suitable non-magnetic material defining a main chamber 12 and at least two spaced apart appendage chambers 13. Chambers 13 extend in the same general direction from one side wall 14 of main chamber 12 and communicating therewith through openings defined by the side wall 14. For enhanced pumping speeds and efficient use of the magnetic circuit 16, the envelope 11 is constructed to define elongated rectangular chambers 12 and 13, with appendage chambers 13 parallelly extending from the side wall 14.

The top end of envelope 11 is closed in end wall 17 suitably sealed to the side walls thereof by, for example, heliarc welding. The end wall 17 is apertured for communicating the interior of envelope 11 to a chamber to be evacuated. The vacuum pump is coupled in gas tight relation to the chamber to be evacuated by a cylindrical tube 18 mounted to end wall 17 enclosing the aperture defined thereby to define therewith a port 19 terminating at a suitable gas tight seal means 20. A convenient gas tight seal means 20 suitable for use with the vacuum pump of the present invention is the ConFlat flange described in the US. Patent 3,208,758 to Carlson et al.

To minimize the pum-ps impedance and optimize the conductance of gas from the main chamber 12 to appendage chambers 13, hence enhance the pumps performance, envelope 11 is constructed to define a rectangular chamber region 21 which extends from main chamber 12 over appendage chambers 13 at the port 18 end of envelope 11. The region between appendage chambers 13 is closed by top plate 25. Additional inter-chamber gas conductance is provided by a passageway 22 between adjacent appendage chambers 13, the passageway 22 extending from the main chamber 12 to the sides of appendage chambers 13 distal main chamber 12. The bottom end of envelope 11 is closed off by an end closing wall 23 sealed to side walls thereof by heliarc welding.

Hence, it is seen that in the most preferred embodiment of the vacuum pump, envelope 11 is an elongated rectangular-like structure defining along at least one elongated side thereof a rectangular re-entrant portion 24.

Vacuum pumping is accomplished by a pump element unit 31 positioned within each appendage chamber 13. A typical pump element unit 31 is shown in greater detail in FIG. 3. The pump element unit 31 includes a cellular anode 32 comprised of, for example, a plurality of parallelly disposed anode cells 33, preferaby circular cylinders, held together in a rectangular-like bunch by spot welds at their tangent points 34. Additional support is provided by a strap 36 tightly wrapped about the circumference of the rectangular-like bunch. The cellular anode 32 is mounted spaced and insulatingly apart between parallelly disposed cathode plates 37 and 38, with the principal axes of the cells 33 perpendicular to the plates 37 and 38. The cathode plates 37 and 38 are constructed from reactive material that is disintegratable upon ion bombardment, erg, titanium. Alternatively, a coating of such material on a support member could serve as a cathode plate. Cellular anode structures other than those formed by individual circular cylinders could be employed, such as rectangular cylinders or any suitable partitioning means defining a plurality of open ended cellular compartments. In all cases where it is desired to take advantage of the benefits derived from confining the glow discharge which takes place in ionic vacuum pumps to a plurality of separate discharges, the anode cells 33 must be open ended separate compartments mounted with a cathode structure covering the open ends of the compartments.

The pump element unit 31 is assembled for use by fixing cathodes 37 and 38 in parallel spaced relation with spacing rods 39 and conductive platforms 41. The spacing rods 39 are secured by bolts at selected locations between the cathodes 37 and 38 proximate the peripheries thereof to extend perpendicularly therebetween. One of the conductive platforms 41 is secured between cathodes 37 and 38 proximate the top end thereof, and the other platform 41 proximate the bottom end thereof by suitable bolts 42. Both platforms 41 serve to electrically connect the cathodes 37 and 38 together and to support the cellular anode 32 positioned between the cathodes. The cellular anode 32 is fixed between cathodes 37 and 38 by rod insulators 43, each secured at one of its ends to strap 36 and at its opposite end to platform 41 by bolts 44.

A pump element unit as described immediately above is commonly classified as a diode element assembly. In some instances, the surface of each cathode facing the cellular anodes 32 is rendered irregular, for example, slotted, in order to enhance the heavy inert gas pumping ability of the pump. Such a pump element unit is described in my US. Patent 3,070,719. Such pump element units are commonly designated as super diode element assembly. Triode element units also are employed to enhance the heavy inert gas pumping ability of pumps. The triode element units differ from the diode element units in that a sputter cathode is interposed the pump envelope walls and cellular anodes. Generally, the sputter cathode electrode is maintained at a negative potential, and the anode electrode and the pump envelope walls at ground potential.

An assembled pump element unit 31 is inserted in nested relation within each appendage chamber 13 with bottom edge of cathodes 37 and 38 resting on the inner surface of bottom wall 23 to support the pump element unit therein. The pump element units 31 are prevented from escaping from the appendage chamber 13 into the main chamber 12 by a retaining plate 46 secured to the inside of wall 14 of the main chamber 12 by nut 47 threadingly engaging a projection (not shown) from wall 14.

A magnetic field of, for example, 1000 gauss is applied perpendicularly to the cathode plates 37 and 38 of each pump element unit 31 (see FIG. 3) by a unique arrangement of U-shaped magnetic circuits 16. Each magnetic circuit 16 includes a permanent magnet 51, an elongated rectangular block in the preferred embodiment, mounted externally of the envelope 11 proximate the wall defining the appendage chamber 13 remote main chamber 12. The north pole N and south pole S of magnet 51 are arranged so that the internal magnetic field of magnet 51 extends in the direction from one cathode side of appendage chamber 13 to the other cathode side thereof. Although a C-shaped magnet could be employed, it has been found to be particularly advantageous from the standpoint of efficient use of magnetic material to employ a straight magnet 51 generating an internal field extending at right angles to the planes within which cathodes 37 and 38 are positioned. In the preferred embodiment, a magnet constructed from heat treated cast Alnico material, consisting of iron, nickel, aluminum and cobalt, Whose magnetic orientation is accomplished during heat treatment is recommended. Such a material is manufactured by Indiana General Corporation of Valparaiso, Ind, under the designation of Alnico VIII and has a residual inductance coefficient of 8.0 kilogauss, a coercive force coefficient of 1600 oersteds and a peak energy product of 5.0x 10 gauss-oersteds. The peak energy product is defined as the maximum external energy that can be maintained by a unit volume of the magnetic material. Permanent magnet materials having a peak energy product equal to at least 5.0 10 gauss-oersteds have been found to be most suitable for use with the vacuum pump of the present invention.

The magnetic circuit 16 for each pump element unit 31 is completed by mounting a first low reluctance material, e.g., soft iron, elongated block pole piece 53 to extend perpendicularly from the north pole of magnet 51. The U-shaped configuration is completed by a second soft iron elongated block pole piece 54 mounted to extend perpendicularly from the south pole of magnet 51 to define with pole piece 53 and magnet 51 a rectangularly -shaped magnetic circuit 16 having an air gap 55 (see FIG. 3). Each magnetic circuit 16 is arranged to receive in its air gap 55 the portion of envelope 11 defining appendage chamber 13 with the pole piece 54 extending into the re-entrant 24.

The magnet 51 and pole pieces 53 and 54 of each magnetic circuit 16 are secured together by two brackets 56, one at the upper end and one at the lower end of magnetic circuit 16. Each bracket 56 has a tab 57 fastened by a bolt 58 to wall 59 of rectangular chamber 21 proximate magnet 51. Extending perpendicularly in a U-shaped array from the side of tab 57 proximate magnets 51 are first, second and third lipped extensions 60, 61, and 62 respectively. The lipped extension 60 secures magnet 51 against wall defining appendage chamber 13 remote main chamber 12. The lipped extensions 61 and 62 respectively secure pole pieces 53 and 54 against the north and south poles of magnet 51. To minimize the flux leakage, magnet 51 is secured between the pole pieces 53 and 54 to have its north and south pole faces abutting the elongated surfaces of the pole pieces defining the air gap 55. By tapering the tips 63 of the pole pieces 53 and 54 at the ends thereof remote from the magnet 51, the field generated by the magnet is concentrated in the gap, the leakage fields are reduced, and the amount of iron, hence the pump weight is reduced. The efliciency of the magnetic circuit 16 can be enhanced further by beveling the corners 65 of pole pieces 53 and 54 distal tips 63.

The above described rectangularly U-shaped magnetic circuit 16 is characterized by efficient use of its magnetic material, enhanced air gap magnetic field intensity profile, and minimized flux leakage. The straight configuration of magnet 51 results in the magnetic lengths through the magnet being the same along all paths in the direction of magnetization. Therefore, it is possible to operate all of the magnets material at a single point on the demagnetization curve. Hence, the operating efiiciency, i.e., maximum air gap field intensity throughout a given air gap size for a given magnet size, of the magnetic circuit 16 is optimized. By tapering the pole pieces 53 and 54, the magnetic circuit surface area of high magnetic potential is reduced, hence leakage flux reduced. Furthermore, the magnetic circuit 16 generates a magnetic field within air gap 55 of essentially constant intensity.

A complete ionic vacuum pump module includes two pump element units 31, each inserted within an appendage chamber 13 positioned in the air gap 55 of a magnetic circuit 16. The adjacent magnetic circuits 16 are arranged with the pole faces of adjacent magnets 51 facing each other being of the same polarity, south as shown in FIGS. 1 and 2. Of course, where pump configurations are needed which have more than two appendage chambers 13 extending from one side of main chamber 12, for example, as shown in FIG. 6, adjacent magnetic circuits 16 having their north poles facing each other will be encountered as well as adjacent magnetic circuits 16 having their south poles facing each other.

The pole pieces extending from the same polarity poles of adjacent magnetic circuits, pole pieces 54 of magnetic circuits 16 in FIGS. 1-2, adjacently extend into the reentrant 24 between adjacent appendage chambers 13. During the operation of the pump, strong magnetic field forces are present which tend to force the adjacent magnetic circuits apart. To prevent movement of the mag netic circuits 16, spacing bars 64 are rigidly fastened, for example, by bolts 66 between the adjacent pole pieces 54 of adjacent magnetic circuits 16 at the top and bottom of the pole pieces 54.

It is seen that with like poles of adjacent magnets 15 arranged proximate, the intense working magnetic fields generated by adjacent magnetic circuit 16 extend in opposite directions. Hence, they do not interlock to establish strong attractive forces which must be overcome when removing the magnetic circuits 16 from the vacuum pump. Therefore, the magnetic circuits can be removed and replaced without having to use special jigs or having to recharge the magnets. Furthermore, with like poles of adjacent magnetic circuits arranged proximate each other, the adjacent pole pieces 54 are at the same magnetic potential. Hence, a single pole pieces 54 can be used in place of the two pole pieces 54 between like poles of adjacent magnetic circuits 16 (see FIG. 4).

With the modular pump configuration of the present invention, the normally considered leakage flux of the magnetic circuits favorably interact with each other and the field established in the air gap of each magnetic circuit. Considering FIG. 2, it is seen that leakage flux in the re-entrant portion 24 between adjacent pole pieces tends to cancel, hence reducing leakage flux or stray magnetic fields. Furthermore, leakage flux from one magnetic circuit 16 permeates the air gap 55 of its adjacent magnetic circuit in the same direction as does the working magnetic field generated by the adjacent magnetic circuit. Hence, the air gap magnetic field established within the air gap 55 of a given magnetic circuit is enhanced by the leakage flux of its adjacent magnetic circuits.

A high voltage insulator 71 penetrates through the cylindrical tube 18 and serves to insulate a high voltage lead 72 from grounded envelope 11. High voltage lead 72 extends into the interior of the pump and connects to a U-shaped conductive bar 73 which in turn is electrically contacted at each of its ends to the strap 36 of cellular anode 32. In this manner, a suitable high positive voltage, e.g., 3000 volts, is applied to cellular anode 32 with respect to grounded cathodes 37 and 38 to initiate the glow discharge therebetween.

In order to secure a plurality of vacuum pump modules together, or mount a magnetic shield to enclose the envelope 11 and magnetic circuits 16, a mounting bar 76 is mounted at each side of envelope 11 adjacent the appendage chamber section. The mounting bar is provided with threaded apertures 77 for receiving suitably threaded bolts therein.

However, more convenient modular embodiments of the vacuum pump of the present invention is shown in FIGS. 57. As shown therein, envelope 11 can be adapted to form any one of numerous configurations depending upon the pumping speed desired. The pumps of FIGS. 5 and 6 have a speed approximately two times those of FIGS. 1, 2 and 4, and the pump of FIG. 7 has a speed of approximately two times those of FIGS. 5 and 6. Considering magnet efficiency, the embodiment of FIG. 6 is preferred to that of FIG. 5, and an embodiment having four units at opposite sides of the main chamber 12 would be preferred to that embodiment of FIG. 6. As can be seen from the figures, any number of appendage chambers 13 can be arranged along any side of main chamber 12. In fact, the appendage chambers 13 could be arranged to extend radially from a circular main chamber 12 like spokes of a wheel.

My making the pump element unit 31 an integral unit and arranging the port 19 to be large enough. to receive a pump element unit 31 therethrough, an ineffective unit 31 can be conveniently replaced by a new unit without having to disassemble the entire pump.

A vacuum pump as shown in FIGS. 1 and 2 having a pumping speed of 270 liters/second was constructed with main chamber 12 being 5 /2 x 9 /4 x 18 /2 inches, the pump element units 31 being approximately 2 /3 x 5% x 14 /2 inches positioned within appendage chamber 13 measuring 2% x 6 x 14 /2 inches, and the cylindrical anodes 33 being 1 /2 inches long and 1 /8 inches in diameter.

In operation, the ionic vacuum pump is evacuated to a pressure of about 10* torrs by a mechanical vacuum pump, not shown. A glow discharge is initiated in the spaces between the cellular anode 32 and cathodes 37 and 38. The glow discharge is subdivided into a plurality of columns defined by the cell openings. Positive ions are created in the glow discharge and are directed to bombard the negative cathodes 37 and 38 thereby disintegrating portions of the reactive cathodes. The disintegrated reactive material sputters from the cathodes of which most is deposited on the large area of the cellular anode 32. Molecules in the gaseou state coming into contact with freshly deposited reactive cathode material are entrapped thereon and effectively removed from the gaseous state thereby evacuating the interior of envelope 11 and other chambers communicating therewith through port 19.

While the ionic vacuum pump of the present invention has been hereinbefore described with respect to selected embodiments, many modifications and variations are possible within the scope of the invention. Therefore, the scope of the present invention is not intended to be limited except by the terms of the following claims.

What is claimed is:

1. An improved ionic vacuum pump comprising an envelope having a port for communicating in gas tight relation with a device to be evacuated and defining a main chamber and a first plurality of spaced apart adjacent appendage chambers interconnected with and extending from said main chamber, anode partitioning means defining a plurality of open ended cellular compartments mounted within each appendage chamber, a cathode structure for disintegration by ion bombardment mounted within each appendage chamber to cover the open ends of said cellular compartments to define therewith a pump element unit, terminal means for connecting a voltage source to establish a potential difference between said cathode structure and said anode partitioning means within each appendage chamber, means for generating a magnetic field in each appendage chamber directed substantially axially of the cellular compartments with the magnetic fields in adjacent appendage chambers in opposite directions.

2. The apparatus according to claim 1 wherein said appendage chambers parallelly extend from one side of said main chamber.

3. The apparatus according to claim 2 wherein said envelope is an elongated tubular member defining elongated main and appendage chamber of rectangular cross section.

4. The apparatus according to claim 3 wherein said means for generating said magnetic fields includes a plurality of U-shaped magnetic circuits, each magnetic circuit comprising an elongated rectangular block magnet and an elongated block pole piece perpendicularly extending from each pole of said magnet in the same direction to define an air gap, each magnetic circuit disposed to receive an appendage chamber in its air gap, adjacent magnets arranged with like poles adjacent each other.

5. The apparatus according to claim 4 wherein said envelope is an elongated rectangular parallelepiped defining at least one re-entrant portion along one elongated side thereof, said re-entrant portion receiving therein two pole pieces of the same polarity one from each adjacent magnetic circuit, the remaining pole piece of one of said magnetic circuits extends along one side of said envelope and the remaining pole piece of the other of said magnetic circuits extends along the opposite side of said envelope, and said pump element units respectively positioned between each one of the sides of said envelope and said reentrant.

6. The apparatus according to claim 5 wherein said open ended cellular compartments of each pump element unit are defined by a plurality of circular cylinders secured together to define an elongated rectangular bunch.

7. The apparatus according to claim 6 wherein said port is larger than said pump element unit.

8. The apparatus according to claim 5 wherein the tips 1 O of said pole pieces remote from said magnets are tapered along the elongated side thereof distal said pump element unit, and the corner of said pole pieces at the end thereof proximate said magnets are beveled along the elongated side thereof distal said magnet.

9. The apparatus according to claim 1 wherein said envelope defines a second plurality of spaced apart adjacent appendage chambers interconnected with and extending from said main chamber, said second plurality of appendage chambers extending from a side of said main chamber opposite said first plurality of appendage chambers.

10. The apparatus according to claim 6 wherein said envelope defines at least a third and fourth plurality of spaced apart adjacent appendage chambers interconnected with and extending from said main chamber, said main chamber a rectangular parallelepiped with different pluralities of appendage chambers extending from different sides thereof.

References Cited DAVID J. GALVIN, Primary Examiner. JAMES W. LAWRENCE, Examiner. S. A. SCHNEEBERGER, Assistant Examiner. 

1. AN IMPROVED IONIC VACUUM PUMP COMPRISING AN ENVELOPE HAVING A PORT FOR COMMUNICATING IN GAS TIGHT RELATION WITH A DEVICE TO BE EVACUATED AND DEFINING A MAIN CHAMBER AND A FIRST PLURALITY OF SPACED APART ADJACENT APPENDAGE CHAMBERS INTERCONNECTED WITH AND EXTENDING FROM SAID MAIN CHAMBER, ANODE PARTITIONING MEANS DEFINING A PLURALITY OF OPEN ENDED CELLULAR COMPARTMENTS MOUNTED WITHIN EACH APPENDAGE CHAMBER, A CATHODE STRUCTURE FOR DISINTEGRATION BY ION BOMBARDMENT MOUNTED WITHIN EACH APPENDAGE CHAMBER TO COVER THE OPEN ENDS OF SAID CELLULAR COMPARTMENTS TO DEFINE THEREWITH A PUMP ELEMENT 